Synthesis and Characterization of Gold Nanoparticles Coated with Ultrathin and Chemically Inert Dielectric Shells for SHINERS Applications

Abstract

We very recently reported a new spectroscopic application for expanding the versatility of surface Raman called "shell-isolated nanoparticle-enhanced Raman spectroscopy" or "SHINERS". The most important and most difficult part of the SHINERS experiment is the effective transfer of the strong electromagnetic field from a gold core through the isolating silica or alumina shell to the probed surface. For this it is essential that the chemically inert dielectric shell be ultrathin (2-5 nm) yet pinhole-free. Herein we describe experimental and theoretical aspects of our SHINERS method in more detail. We provide a protocol for the synthesis and characterization of optimized shell-isolated nanoparticles (SHINs), and we examine the advantages of SHINERS nanoparticles over bare gold nanoparticles. We also present high-quality Raman spectra obtained from gold and platinum single-crystal surfaces in an electrochemical environment by our SHINERS technique. SHINERS is a simple and cost-effective approach that expands the flexibility of surface-enhanced Raman scattering (SERS) for an unprecedented diversity of applications in materials and surface sciences.

Silver Nanorods Wrapped with Ultrathin Al2O3 Layers Exhibiting Excellent SERS Sensitivity and Outstanding SERS Stability

“…Therefore, it can be used as a mark to check out whether the Al 2 O 3 coating layers were compact enough to protect Ag nanorods. If there are any pinholes in the Al 2 O 3 layer, pyridine could penetrate through pinholes and be adsorbed on the surface of Ag nanorods, thus exhibiting Raman siganls 46 47 48 . We dipped the as-prepared Ag nanorods (uncoated, and coated by 1, 2, 3 and 5 ALD cycles) into a 1 × 10 −2 M pyridine solution, and measured the Raman spectra.…”

Shell‐Isolated Nanoparticle‐Enhanced Raman Spectroscopy (SHINERS)

“…We call this new technique "shell-isolated nanoparticle-enhanced Raman spectroscopy" (SHINERS) [45][46][47], which very recently has been applied successfully to several systems. [45][46][47][52][53][54][55][56][57][58][59][60][61][62][63].…”

Pinhole-Containing, Subnanometer-Thick Al2O3 Shell-Coated Ag Nanorods as Practical Substrates for Quantitative Surface-Enhanced Raman Scattering

“…To further confirm whether Al 2 O 3 shells were compact enough, we introduced pyridine and acridine, 24,25,47,48 two probe molecules that can directly contact the Ag surface instead of Al 2 O 3 . If there are any pinholes in the Al 2 O 3 shell, pyridine/ acridine would penetrate through the pinholes and be adsorbed on the surface of Ag NRs, thus exhibiting Raman signals.…”

“…If there are any pinholes in the Al 2 O 3 shell, pyridine/ acridine would penetrate through the pinholes and be adsorbed on the surface of Ag NRs, thus exhibiting Raman signals. 24,25,49 As illustrated in Figure 2a The Journal of Physical Chemistry C Article Chemical Stability Evaluation. To function as routine SERS sensors, they should possess superior stability at practical conditions even for erosive environments.…”